This invention relates to a fluidic seal for use in a gas turbine engine and, more particularly, to a fluidic seal between arcuate segments of the stator-nozzle assembly.
In large turbojet and turboshaft engines, the nozzle-turbine section is of relatively complex construction. For example, the nozzle diaphragm is comprised of a plurality of circumferentially spaced airfoils extending radially inward from an outer circumferentially annular band. More particularly, the nozzle diaphragm is formed of a series of arcuate nozzle diaphragm segments joined together each including a band portion and a plurality of airfoils. This type of construction usually requires a number of closely machined mating surfaces between nozzle diaphragm segments and sealing means to deployment between the surfaces.
Conventional seals have long been employed between adjacent arcuate nozzle segments. These conventional seals can all be characterized as tangential seals since they extend in a tangential or circumferential direction to seal a tangential or circumferential gap between adjacent nozzle diaphragm segments. Various problems arise with seals employed in this manner. First, thermal growth of the arcuate sections of the nozzle diaphragms is greatest in the circumferential direction. Hence, the gap across which the seal is disposed is widely variable in dependence upon the temperature of the nozzle segments. In order to be effective a seal must be relatively insensitive to variations in gap width which occur with variations in temperature. While prior art seals have approached this problem by providing free-standing seals which reside in an oversized slot and which are designed to extend fully across the gap at its maximum width, such seals have exhibited excessive fluid leakage over the wide range of pressure drops typically encountered by the seal. The excessive leakage results, in part, from resonant vibration of the free-standing seal which causes the seal to lift from its sealing surface.
Another difficulty encountered arises from practical constraints associated with assembly of the nozzle diaphragm into the turbine section. In many instances assembly of adjacent nozzle segments cannot be accomplished by axial insertion since adjoining portions of the turbine structure restricts axial access. While previous attempts have been made to provide a sealing structure which would be compatible with radial insertion, such attempts have not proven to be completely commercially satisfactory because of the intricacy of the design and its associated excessive cost. One such attempt, shown in U.S. Pat. No. 3,728,041 discloses angled cavities in each segment inclined to the segment surface at an angle not less than the angle of intersection of the plane of insertion of the adjacent segment.
Therefore, it is an object of this invention to provide a sealing arrangement between the interfaces of a segmented nozzle diaphragm wherein the effectiveness of the sealing member is relatively insensitive to the arcuate thermal growth of the arcuate nozzle-diaphragm segments.
It is another object of this invention to provide such a sealing arrangement that is effective to prohibit fluid leakage over the wide range of pressure drops typically encountered in the turbine nozzle section of a gas turbine engine.
It is yet another object of the present invention to provide an inexpensive sealing arrangement which is easily compatible with assembly constraints associated with the turbine section of a gas turbine engine.